Postretirement Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cost of pension plans:
Service cost for benefits earned	$ 28,201	$ 30,433	$ 22,510
Interest cost on benefit obligation	33,125	30,755	28,112
Expected return on plan assets	(39,520)	(35,921)	(31,419)
Prior service cost amortization	696	670	712
Net actuarial loss amortization	8,111	14,031	6,344
Pension plan cost	$ 30,613	$ 39,968	$ 26,259
Erie Insurance Exchange (EIE)
Postretirement benefits
Postretirement annual benefit expense reimbursed to Indemnity from the Exchange (as a percent)	59.00%
Erie Family Life Insurance Company (EFL) | Employee pension plan
Postretirement benefits
Contingent liability for amount of nonparticipating annuity contracts the employee pension plan purchased from EFL	$ 21,000